rating component cleanup
cleanup the tooltip directive
cleanup the category filter
cleanup ch06 & 07 components
cleanup routing
cleanup service
misc minor cleanup
Update ch07 README.md

based on previous chapter templates
Merge pull request #92 from vicb/cleanup

Some cleanup across all chapters
refactor(ch07): simplify code

see https://github.com/angular/angular.dart.tutorial/pull/92#discussion-
diff-10179304